The subject matter disclosed herein relates to power converters and, in particular, to protecting power converters from fault currents.
Power converters (also known as inverters) are utilized to convert direct current (DC) into alternating current (AC). Power converters have fault modes that can allow destructively high fault currents to flow through them. The fault currents can be large enough to damage the bus structure of the power converter or destroy or otherwise damage power semiconductors (e.g., integrated gate commutated thyristors (IGCTs)) in the fault path. In order to limit the peak value of the fault current through the power converter and devices therein, the fault current must either be interrupted or diverted.
Fuses are one method of interrupting the fault current. The fuses can be installed between the DC link capacitors and the phase legs of the power converter. Another approach is to utilize a so-called “current crowbar.” One type of current crowbar utilizes a high-speed silicon controlled rectifier (SCR) that is turned on in the event of a detected fault current. When the current crowbar is activated it provides a low impedance path that diverts fault current away from the phase legs of the power converter. An activated current crowbar also provides a low impedance pathway for discharging the DC link capacitors.
The gating of the SCR is typically controlled by circuits that sense the rate-of-change of current in a conductor in the DC link assembly. The rate-of-change of current is compared it to a threshold and the current crowbar is activated when the rate exceeds a threshold level. Such a control circuit requires a separate control rack and sensors.